In-body sensor networks are those networks where at least one of the sensors is located inside the human body. Such wireless in-body sensors are mainly used for medical applications, collecting and monitoring important parameters for health and diseases treatment. The IEEE Standard 802.15.6-2012 for Wireless Body Area Networks (WBAN) considers in-body communications in the Medical Implant Communication Service (MICS) band. Nevertheless, high data rate communications are not feasible at the MICS band due to its narrow occupied bandwidth. In this framework, Ultra-Wideband (UWB) systems have emerged as a potential solution for in-body high data rate communications, due to its miniaturization capabilities or low power consumption. In the last years, some open issues have determined the research about in-body propagation. Firstly, the propagation medium, i.e., the human body tissues, is frequencydependent and exhibits a large attenuation at UWB frequencies. Secondly, the behavior of the in-body antennas is highly dominated by the surrounding tissues. Thus, the in-body channel characterization in UWB depends not only on the channel behavior itself, but also on the methodology of characterization. This paper intends to outline the research performed in the field of UWB in-body radio channel characterization considering the propagation medium, as well as the methodology of analysissoftware simulations, phantom measurements, in vivo measurements-. Thus, authors provide an overall perspective of the current state of the art, limitations for the analysis of in-body propagation, and future perspectives for UWB in-body channel analysis.
Wireless Body Area Networks (WBANs) are a promising technology for medical purposes. Currently the WBAN are classified into: implanted (in-), surface (on-) or outside (off-) body communications regarding the location of the devices with reference to the human body. The Ultra Wide-Band (UWB) frequency band is growing as a band of interest for implanted communications because of its high data rate and low power consumption among other benefits. Software simulations, in-vivo measurements and experimental phantom measurements are common methods to properly characterize the propagation channel. Nevertheless, up to now, experimental phantoms measurements presented in the literature show some inconveniences, i.e., the accuracy of the phantoms compared with the real human tissues or the testbed used for the measurements. This paper aims at overcoming these issues using accurate phantoms designed for the purpose of implanted communications in the UWB frequency band. In addition, a multilayer phantom container was developed. This container has capacity for two different phantoms, emulating a heterogeneous propagation medium for in-body measurements. Moreover, a novel setup was built for in-body phantom measurements. As a result, an experimental path loss model is presented from the measurements obtained with phantoms. Besides, software simulations mimicking the experimental setup are performed in order to validate the previous results obtained.
Localization inside the human body using ultrawideband (UWB) wireless technology is gaining importance in several medical applications such as capsule endoscopy. Performance analysis of RF based localization techniques are mainly conducted through simulations using numerical human models or through experimental measurements using homogeneous phantoms. One of the most common implemented RF localization approaches uses the received signal strength (RSS). However, to the best of our knowledge, no experimental measurements employing multilayer phantoms are currently available in literature. This paper investigates the performance of RSS-based technique for two-dimensional (2D) localization by employing a two-layer experimental phantom-based setup. Preliminary results on the estimation of the in-body antenna coordinates show that RSS-based method can achieve a location accuracy on average of 0.5-1 cm within a certain range of distances between in-body and on-body antenna.
This paper presents in-body to on-body and inbody to in-body channel models of a planar wideband elliptical ring implanted antenna in the lower part of Ultra-WideBand (UWB, 3.1 to 5.1 GHz). The results are verified inside a practical UWB liquid phantom with the help of a wideband on-body monopole antenna. Moreover, the design principle of the inbody and on-body antennas, as well as their simulated and measured reflection coefficients are presented. The channel characterization inside the lossy medium gives a deep insight of wireless capsule endoscope technology (WCE) and helps to evaluate the radiation performance of the previously designed planar elliptical ring implanted antenna.
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